Solar Energy from Rain

26 September 2016

While solar energy provides consumers with a renewable and sustainable source for their electricity needs, adverse weather conditions can limit solar panels from producing as much energy as they could in normal conditions, reducing their efficiency. During bad weather, stored energy within the system can be used initially, but further energy may draw from local utility when there is not enough solar power available.

It is estimated that 10 - 25% less energy is produced by solar panels on cloudy days compared to clear, sunny days. Given the variability of solar panels performance in bad weather, combined with the rapid depletion of conventional energy sources and the environmental degradation caused by their exploitation, further resources must be developed.

Producing Energy from Rain

As research in the field of solar energy continues to advance, the potential of photovoltaic cells to produce energy from raindrops has been explored.

Composed primarily of dissolved particulate materials and gasses within the atmosphere, rain is water that falls under gravity in the form of droplets. Various salts are present within raindrops, including sodium, calcium, and ammonium, which are all split into positive and negative ions.

As a result of this chemical composition, researchers at Ocean University in Qingdao, China believe they can manipulate the ionized components of rain to harness a simple chemical reaction, which could generate electricity.

Graphene All-Weather Solar Panels

By adding an ultra-thin layer of electron-enriched graphene as a top layer to the all-weather solar panels, the ions present within raindrops are able to react with the layer of graphene to produce energy.

Made up of a single layer of bonded carbon atoms, graphene’s superb properties of conductivity and transparency allow light to penetrate panels in order to produce an electric current within the solar cell. In weather conditions where rain is present, graphene binds its electrons with the positively charged ions present within the rain drops in a process known as the Lewis-acid base reaction.

At this point of contact, where natural free-flowing water and graphene are bound, the water becomes enriched in positive ions as the graphene becomes enriched in delocalized electrons. This collision produces a double-layer composed of electrons and positively charged ions, often called the pseudocapacitor, where the difference in potential is enough to produce a voltage and current for energy production.

In what researchers from Ocean University are calling “all-weather solar cells,” this solar cell offers a unique long-term stability component for solar panels that can be excited by both sunlight and rain. Despite their promise, graphene-coated solar cells are only able to transform 6.5% of the energy generated into electricity, whereas most solar panels are able to convert around 22.5%.

Further research into graphene’s full potential for solar energy purposes could have profound implications for the future of sustainable energy.

Rainwater Harvesting

While the utilization of rain as a secondary source of energy is still in the early stages of development, the performance of a hybrid solar-wind-energy system has existed for several years in a continued effort to enhance energy production.

Through the optimization of the five primary green technologies - wind turbines, solar photovoltaic system, rainwater harvesting and utilization system, natural ventilation and roof sky lighting - this system is a great alternative to produce efficient energy, especially for use in large buildings.

As the wind turbines and solar photovoltaic panels generate and store energy in batteries for future building usage, rainwater within this hybrid system is harvested for recovering energy.

Rainwater harvesting has been found to be a logical solution for both renewable energy purposes, as well as a way to address water resource challenges in certain areas of the world. Within this hybrid system, rainwater is collected from the roof into two water storage tanks, where the secondary water storage tank receives extra rainwater only once the primary are full.

As rain is collected, energy consumption is reduced, which is especially important for use in high-rise buildings that require water pumping. This rainwater storage system integrates an automatic cooling and cleaning system, where a constant stream of water has been designed to clean and cool the roof, which also improves the electrical efficiency of the solar photovoltaic system.

Whether rain is stored as a supplement to existing energy systems, or the specific ionization components of a raindrop can enhance the energy production of solar energy panels, the future of rain as a renewable energy source shows great promise.